Determination of MEA-nitramine in Soil Water and Assessing the Sorption Potential of MEAnitramine to Soil

Sammendrag

Small amounts of amines are emitted with the flue gas from amine based carbon capture plants. The amines atmospheric degradation have been studied in detail. The environmental impact of the degradation products, e.g. the possibly carcinogenic and mutagenic nitramines, is however insufficiently studied. This thesis investigates the capacity of nitramines to sorb to soil, depending on the soils physiochemical characteristics. To accomplish this, the analytical challenges with regards to determination of nitramines in soil water had to be solved. Soil samples were collected in the vicinity of Technology Center Mongstad (TCM) (~15 km) as this is a possible future deposition site for nitramines. The sampling sites were chosen with the aim of collecting soils with different physiochemical properties, with special emphasis on the content of soil organic matter and soil texture. All of the collected soil samples (n=16) were analysed for explanatory parameters expected to influence soil sorption, such as organic matter (OM) content, dissolved natural organic matter (DNOM) leached from the soil, texture, mineralogy, pH and conductivity. A selection of the samples (n=5) were used in soil sorption experiments to assess the sorption potential of N-Nitroethanolamine (MEA-nitramine). A batch experimental set-up was used, and sorption was measured as loss of MEA-nitramine from the aqueous phase after being added at known concentrations (24 h equilibrium). For these samples, elemental composition was also determined. Possible correlations between the sorption coefficients and the soils physiochemical characteristics were assessed. Determination of MEA-nitramine in soil water with LC-MS/MS proved to be a challenge due to matrix effects. Different calibration methods with and without matrix matched calibration solutions were tested. Another nitramine, N-nitromethylamine (MMA-nitramine), was tested as internal standard. Additionally, a couple of sample pretreatment techniques were tested to try and separate the analyte from the matrix (solid phase extraction (SPE), filtration). Sorption partitioning coefficients between soil and aqueous phase were determined (Kd) and the results imply that a significant amount of MEA-nitramine will remain in the aqueous phase. Correlation between the partition coefficients for the five studied soils and the soils OM content was observed (r > 0.788). Loss of internal standard (MMA-nitramine) was also observed, this loss correlated strongly with the DNOM concentration in the sample supernatant (r = 0.9924), implying that sorption to DNOM could be important. The relation between sorption and OM content implies that sorption will generally be higher in the top soil (organic) horizons than in the lower (mineral) soil horizons. As deposition of atmospherically formed nitramines will be to the soil surface, this can serve to hinder mobility. The analytical determination method for nitramines in soil water was improved, although not considered satisfactory at the end of the study. Major improvement resulted from the used of matrix matched calibration curves, which compensate for both ion suppression/enhancement effects and possible sorption to DNOM. Even though this is time- and labour consuming, the method was proven more successful than attempts made to separate the analyte from the matrix prior to analysis. The used of MMA-nitramine as an internal standard for determination of MEA-nitramine was not successful, possibly due to the difference in retention time and therefore possible different effect from the matrix components. An isotope-labelled internal standard should therefore be acquired. Investigation into other sample pretreatments could also be of interest. Note that previously reported sorption partition coefficients for sorption of nitramines to soil could be inaccurate if matrix matched calibration curves were not employed.